Zombie Headz of Mirrah dual wields a double Scythe of Want for this tutorial including power stance, in Dark Souls 2.

To use Power Stance - You need to have 150% of the STR and DEX requirements (of the larger weapon when using different weapons) in your stats. For example: To use power stance with a weapon requiring 20 STR and 14 DEX your character's stats need to be 30 STR and 21 DEX.